Retractable cannula for surgical procedures

ABSTRACT

A cannula assembly having a plurality of outwardly-biased flexible fins capable of inward movement such that the fins converge upon insertion of a trocar device. The fins include a slot formed therein, with a corresponding raised feature on the trocar shaft capable of engaging the slots. Inward movement of the trocar within the cannula lumen causes the fins to converge. An additional embodiment utilizes outwardly-biased flexible fins that lock together in a closed position, with corrugated features in the fin inner surface that contact the trocar shaft such that, upon insertion of the trocar, the fins unlock and splay outward.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/882,030, filed on Sep. 14, 2010.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to devices for performing percutaneoussurgeries and, more specifically, to surgical cannulae.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 1.98

Traditional minimally-invasive arthroscopic surgeries are performedusing a cannula device to penetrate small incisions in the patient'sskin and outer tissue, creating a port through which surgical tools maybe passed to allow access to the underlying structure of interest. Forexample, in shoulder arthroscopy, the procedure is performed through“portals” in the patient's skin. These portals are formed from smallincisions, generally about 1/2of an inch to an inch long in the skin,and are located over particular areas of the joint that the surgeon willneed to operate upon. Cannulas are then inserted into the portals sothat instruments can easily be placed in the shoulder joint. Shoulderarthroscopy itself involves inserting a specially designed video camerawith a very bright fiber optic light source into the shoulder joint sothat the important parts of the joint can be seen. Instruments that havebeen specially designed to remove inflamed tissue, attach sutures tobone, and repair tears and damaged tendons are then used to operateinside the shoulder.

The area between the skin tissue and shoulder joint is quite small.Consequently, it is necessary to “inflate” the area by pumping salinefluids into the joint under pressure. This pressure pushes the tissueoutward from the joint and allows greater room for manipulation of thearthroscopic camera and other surgical tools. However, the actualworking angle of the tools is ultimately determined by the length andinner diameter of the cannula. Heavy patients or patients with largeamounts of skin and other tissue covering the joint require a longercannula to penetrate the tissue sufficiently for the procedure. Thisincreased cannula length decreases the working angle of the tools at thejoint, limiting the ability of the surgeon to perform the procedure.Although this angle may be increased by increasing the inner diameter ofthe cannula, there are realistic limits on the useable diameter. Forexample, the diameter can only be increased by a small amount or else itwould effectively eliminate any benefit of conducting the arthroscopicprocedure as the portal size could become the equivalent of a largeincision as performed in traditional surgery.

What is needed is a cannula device that is capable of compressing thetissue through which it penetrates, and that is relatively simple toinsert and remove so as to minimize tissue damage to the patient.

BRIEF SUMMARY OF THE INVENTION

A cannula assembly, the assembly comprising: a body member including aproximal end, a distal end, and a lumen extending therebetween, thedistal end including a plurality of outwardly-biased flexible finsextending therefrom, each fin capable of inward movement such that thefins converge, each fin further including a wall formed from an innersurface and an edge surface extending from the inner surface to an outersurface, and at least one longitudinal slot formed within the fin walland extending to a surface; and a trocar device including a proximal endand a shaft extending therefrom to form a distal end, the shaft memberincluding at least one raised member per fin slot, each raised memberbeing radially disposed proximate the distal end, the shaft membercapable of insertion into the lumen, wherein insertion of the shaftwithin the lumen engages the raised members with the fin slots causinginward movement of the fins.

A cannula assembly, the assembly comprising: a body member including aproximal end, a distal end, and a lumen extending therebetween, thedistal end including a plurality of outwardly-biased flexible finsextending therefrom, each fin capable of inward movement such that thefins converge, each fin further including a wall formed from an innersurface and an edge surface extending from the inner surface to an outersurface, and at least one longitudinal slot formed within the wall andedge surface; and a trocar device including a proximal end and a shaftextending therefrom to form a distal end, the shaft member including atleast one raised member per fin slot, each raised member being radiallydisposed proximate the distal end, each raised member cross sectionapproximating the shape the fin slots, the shaft member capable ofinsertion into the lumen, wherein insertion of the shaft within thelumen engages the raised members with the fin slots causing inwardmovement of the fins such that the fins converge.

A cannula assembly, the assembly comprising: a body member including aproximal end, a distal end, and a lumen extending therebetween, thedistal end including a plurality of outwardly-biased flexible finsextending therefrom, one fin including a locking feature at its distalend, wherein the other fins may be captured beneath the locking featureclosing off the lumen; a trocar device including a proximal end and ashaft member extending therefrom to form a distal end, the shaft membercapable of insertion into the lumen; and an anti-plunging deviceremovably attachable to the shaft member wherein the attachedanti-plunging device blocks the shaft member from advancing past a firstposition within the lumen, and wherein removal of the anti-plungingdevice allows the shaft member to advance past the first position to asecond position wherein the fins unlock and move outward.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The present invention will be more fully understood by reference to thefollowing detailed description of the preferred embodiments of thepresent invention when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an exploded view of a first embodiment of the cannulainvention;

FIG. 2 is an assembled view of the embodiment, highlighting a crosssectional area;

FIG. 3 is a cross section of the working end of the invention as in theassembled view of the embodiment;

FIG. 4 is a depiction of the cannula invention prior to insertion of thetrocar device;

FIG. 5 is a depiction of an alternative embodiment of the cannulainvention prior to insertion of the trocar device;

FIG. 6 is an assembled view of the alternative embodiment, highlightinga cross-sectional area;

FIG. 7 is a cross section of the working end of the invention as in theassembled view of the alternative embodiment;

FIG. 8 is a cross section of the working end highlighting an alternativedovetail channel shape;

FIG. 9 is a cross section of the working end highlighting an alternativecircular channel shape;

FIG. 10 is a cross section of the working end highlighting analternative embodiment with an embedded material that assists in theopen bias of the fins;

FIG. 11 is an alternative embodiment of the cannula invention with thefins in the open position;

FIG. 12 is a depiction of the process for closing the fins in thealternative embodiment;

FIG. 13 is a depiction of the alternative embodiment of the cannulainvention prior to insertion of the trocar device; and

FIG. 14 is a cutaway view of the invention in use during shouldersurgery.

The above figures are provided for the purpose of illustration anddescription only, and are not intended to define the limits of thedisclosed invention. Use of the same reference number in multiplefigures is intended to designate the same or similar parts. Furthermore,when the terms “top,” “bottom,” “first,” “second,” “upper,” “lower,”“height,” “width,” “length,” “end,” “side,” “horizontal,” “vertical,”and similar terms are used herein, it should be understood that theseterms have reference only to the structure shown in the drawing and areutilized only to facilitate describing the particular embodiment. Theextension of the figures with respect to number, position, relationship,and dimensions of the parts to form the preferred embodiment will beexplained or will be within the skill of the art after the followingteachings of the present invention have been read and understood.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts an exploded view of a first embodiment of the cannulainvention. As shown in this figure, the complete apparatus includes acannula device (102) and a trocar device (120). The trocar device (104)includes a handle (120) at its proximal end with a shaft member (118)extending therefrom to form a distal end with a defined tip (124). Alongthe shaft are multiple raised members (122) that protrude essentiallyradially from the axial center of the shaft (118) and that extendlongitudinally along the shaft length. The raised members (122) in thepresent embodiment are depicted as extending approximately one half ofthe length of the shaft (118) near the distal end. However, the lengthof the raised members (122) may vary in other embodiments. For example,the raised members (122) in another embodiment may be wider than theyare in length. Such alternate lengths are within the scope of thepresent invention. The raised member (122) of the embodiment, asdepicted, is also a single element. However, in another embodiment theraised member may be split in to portions such that, on the whole, theraised member (122) may still engage the corresponding slot.

The present embodiment of the cannula device (102) includes body member(108) having a proximal end and a distal end. The body member (108) isessentially cylindrical in shape, having a lumen extending from end toend. Although the body member in the present embodiment is essentiallycylindrical in shape, other embodiments may have a geometric crosssectional shape other than circular, or may include a mix of circularand other geometric shape such as a circular lumen cross section with ageometric outer wall cross section or vice versa. The outer wall mayalso include a ribbed, grooved, or helical raised feature (or even arecessed feature) that assists the device in gripping a patient's skinand muscle tissue for device retention. Such alternate embodiments areenvisioned and are within the scope of the present invention.

The proximal end includes a fluid drain port (110) and a proximal collar(114) that retains several silicon discs (112) that are used as fluidseals through which surgical instruments may pass. The proximal collar(114) attaches to the proximal end of the body member for positiveretention of the silicon discs (112). The drain port (110) allows forfluid management during surgical procedures in the same fashion asconventional cannula devices.

The distal end of the body member (108) includes a plurality offlexible, yet semi-rigid fins (106) that are formed in theoutwardly-biased position as shown during injection molding of thedevice. The present embodiment utilizes medical grade polymers duringthe injection molding or extrusion process. These polymers allow thefins to retain the outwardly-biased shape at normal operatingtemperatures for the device, yet also allow the fins to flex inwardlywhen sufficient pressure is applied. For example, polyurethanes such asHytrel® or Arnitel® may be utilized due to the desired durabilitycharacteristics, or PVC if expense is a concern.

Each fin (106) of the present embodiment includes a radius of curvaturethat approximates that of the wall of the body member (108) that formsthe lumen. When the fins (106) are forcibly moved to the inward position(as depicted in FIG. 2), the inner surface of the fins essentiallyextends the lumen of the body member (108) to the distal end of thefins. Further, because the fins have a wall thickness, each fin featuresan edge surface that extends from the fin inner surface to the fin outersurface. It is the edge surface of the fin that contacts the edgesurface of the adjacent fin when the fins are in the inward-mostposition (as in FIG. 2).

FIG. 2 depicts the cannula invention prior to insertion of the trocardevice. As shown, the tip (124) of the trocar device is inserted throughthe cannula device proximal collar (114) such that the raised members(122) engage with complimentary slots formed within the body member(108) of the cannula device. These complimentary slots extend a distancewithin the cannula device lumen and along the edge surfaces (126) of thefins (106). This embodiment features two corresponding slots (126), onefor each fin. Other embodiments may utilize a greater number of finsand, consequently, would require a correspondingly greater number ofslots. For example, an embodiment with three outwardly-biased fins wouldhave three pairs of adjacent fin edge surfaces. Such an embodiment wouldrequire three slots within the cannula body member and threecorresponding complimentary raised members on the trocar device.

FIG. 3 depicts an assembled view of the embodiment as it would beconfigured for use once the trocar device (120) is inserted into thecannula device body member (106). As shown, insertion of the trocardevice (120) engages the slots within the fins (106), causing the fins(106) to move inward against the outward bias pressure that is normallypresent. In the full inward position the edge surfaces of the fins (106)meet. This figure also highlights a cross sectional area, which is shownin detail in FIG. 4.

The cross section detail depicted in FIG. 4 demonstrates how the trocarshaft member (118) fits within the cannula lumen and engages thecomplementary slots in the fins (106). In this embodiment, the cannuladevice has two fins. Formed within the inner wall of the body member aretwo slots, each having a cross section that resembles a serif fontcapital letter “T”. This slot extends the length of the body memberinner wall and is aligned with the origin of the edge surfaces of thefins (106) as they extend from the body member, and accepts acorresponding serif font capital letter “T” shaped raised member (122)on the trocar.

A corresponding portion of the “T” slot is formed in the wall of eachfin at the junction of the edge surface and the inner surface. When thefins (106) are in the inward most (or “closed”) position (as shown inFIG. 3), the adjoining fin edge surfaces (126) meet and complete theoverall “T” slot such that it extends from the body member to the distalend of the fins. Although the corresponding “T” slot portion in the finedge surfaces (126) extends approximately the entire length of the finin the present embodiment, other embodiments may extend less than theentire length of the fin.

To prepare the embodiment for use with a patient, the trocar device isinserted into the cannula device lumen such that raised members (122)engage the corresponding and complimentary body member “T” slots. As thetrocar shaft (118) is further inserted into the lumen, the raisedmembers slide within the “T” slots until they reach the origin of theedge surfaces of the fins (106). As the trocar is further inserted, theraised members apply stress to the corresponding “tail” elements of “T”slot portions in each fin edge surface (126) causing the fins to moveinward and come together along adjacent edge surfaces. This has theeffect of “zipping” the fin edges together for insertion of the deviceinto a patient.

Although a serif capital “T” shaped slot cross section is discussed,other embodiments may utilize cross-sectional slot shapes that providean elemental feature that positively engages and accepts compressivestresses from the corresponding elements of the raised members to causethe fins to move inward and come together along adjacent edge surfacesas the trocar is inserted. Each fin edge surface may include a slot thatfeatures a cavity that is larger than the opening formed in the edgesurface, with additional material removed from the edge surface where itintersects with the fin inner surface to allow for the correspondingraised member to pass therebetween. For example, the edge surface mayhave a longitudinal slot formed therein that has a dovetailcross-section. The corresponding raised member would include twocorresponding dovetail pin features to engage the adjacent dovetailslots in the adjacent fin edge surfaces. Each fin edge surface may alsoinclude a slot with a formed cavity that turns inward towards the innersurface, outward towards the outer surface, or both, such that the slotopening in the edge surface is not aligned with the deepest portion ofthe slot cavity. For example, the edge surface may have a longitudinalslot that is formed such that cavity beneath the slot opening iscentered toward the inner surface and does not share the exactcenterline of the cavity opening. Again, the trocar device would includea corresponding raised member that engages the slot as before. In yetanother embodiment it is also possible to have a plurality of slots,with each slot having a different geometric cross sectional shape.

Once inside a patient, the trocar is removed from the cannula device andthe fins naturally return to their outwardly-biased position. FIG. 14depicts such an event. As shown, the body member (108) forms a port inthe patient's skin and outer tissue (1406) through which surgicalinstruments (1402) may pass. The outwardly-biased flexible fins (106) ofthe cannula device exert pressure on the tissue (1406) and assist thesurgeon in compressing the tissue (1406) to allow for a greater workingcavity (1404) and exposure of the surgery site (1408). Because of thecompressive effect of the flexible fins (106) on the tissue (1406), thelength of the body member (108) may be made relatively short compared toconventional cannula devices. This shortened body member (108) resultsin a shortened lumen length that, consequently, allows a greater workingangle (shown on the figure as the Greek letter “a”) for the surgeon'stools (1402), which improves the surgeon's access to the surgery siteand reduces the need for physical manipulation of the cannula duringsurgery. When surgery is complete, the cannula device may be removed byreinserting the trocar device into the lumen such that the trocar raisedmembers engage the slots in the fins and the fins move inward once more.The cannula device may then be withdrawn from the patient with minimaltissue damage. Although the present embodiment is described in useduring shoulder arthroscopy, one of ordinary skill will understand thatthe device may be employed in essentially any arthroscopic,laparoscopic, or other surgery requiring the surgeon to establish aworking port in the tissue of a patient.

FIG. 5 depicts an alternative embodiment of the cannula invention priorto insertion of the trocar device. As shown, the trocar device has ashaft member (510) with raised members (506) and a distal tip (508).However, in this embodiment the corresponding slots in the cannuladevice are formed such that they extend from the proximal opening andalong the inner wall of the body member and along the inner wall of thefins (502) at some point between each fin's edge surface (504).Insertion of the trocar device into the cannula device, once again,causes the flexible outwardly-biased fins 502) to move inward such thatadjacent fin edge surfaces meet and the closed fins essentially form anextension of the body member as shown in FIG. 6. In this figure, thedevice is again ready for insertion into a patient.

FIG. 6 depicts an assembled view of the alternative embodiment,highlighting a cross sectional area. FIG. 7 depicts the cross section ofthis embodiment in which conventional “T” slots (504) are formed in thefin (502) inner walls approximately midway between the edge surfaces.The trocar shaft (510) features raised members (506) that correspondwith each “T” slot. Although the present embodiment depicts a singleslot formed midway between the edge surfaces of each fin, otherembodiments may utilize multiple slots per fin, with appropriate spacingbetween the slots. In such embodiments, the trocar shaft will featurecorresponding raised members that engage the slots. Further, althoughthe present embodiment describes use of “T” slots in the fins, othergeometric slot shapes that afford positive engagement with correspondingraised members may be utilized. For example, FIG. 8 depicts use ofdovetail slots (802) formed in the inner surfaces of the fins (502).Likewise, FIG. 9 depicts use of circular slots (902) formed in the innersurfaces of the fins (502). Still other geometric slot shapes arecontemplated and are within the scope of the present invention. Further,it is possible to combine fin edge surface slots with inner surfaceslots. Such an arrangement may be helpful to more evenly distribute theclosing forces applied to the fins during insertion of the trocar deviceand prevent distortion of the fins.

In yet another embodiment, it is possible to utilize an embedded shapememory alloy as a biasing device, such as but not limited to Nitinol, ineach fin to increase the outward-bias pressure generated by the fins. Byincreasing the outward bias pressure, it is possible to apply additionalcompressive stress to the tissue of the patient through which thecannula device is inserted. FIG. 10 depicts such an embodiment. Asshown, each fin (106) includes an embedded shape memory alloy strip(1002) within the fin wall at some location between the edge slots(126). This embedded shape memory alloy strip may also be used with thealternative embodiments discussed above, and may be incorporated withinthe wall beneath or near the respective slot. Further, although thefigure depicts use of a single embedded shape memory alloy (1002) ineach fin (106), other embodiments may utilize multiple shape memoryalloys at various locations spaced within the fin walls. Other biasingdevices may include other metals, such as stainless steel, or polymersthat exert added biasing pressure over that provided by the molded fins.

In yet another embodiment it is possible to incorporate an additionalalloy with the embedded shape memory alloy to create a bimetallic stripor alter the composition such that it varies, with temperature, the finoutward-bias pressure that is generated. For example, Nitinol may alsobe “tuned” to react at different temperatures by adding additionalalloys to its composition. Such a material may be used in the fins of anembodiment to allow the fins to generate greater outward-bias pressureswhen the fins reach the patient's body temperature.

FIG. 11 depicts an alternative embodiment of the cannula device of thepresent invention. As shown, the cannula device features a body member(1102) with a lumen that exists from the proximal end to the distal end,and a plurality of outwardly-biased fins (1104) extending from thedistal end of the body member. Each fin includes a plurality ofcorrugated features (1110) that extend inward from the outer surface ofthe fin and are formed along the length of the fin. One fin includes alocking feature (1106) at its distal end for capturing the distal end ofthe other fins (1108). The locking feature in this embodiment is aconical portion of the distal end of the fin that allows the distal endof the other fins to be captured beneath.

This embodiment of the device is prepared as shown in FIG. 12. Asdepicted, the fins are physically moved inward such that the adjacentfin edges meet and a fin grouping is formed. The fin grouping is thenbent toward the fin having the locking feature such that the fin withthe locking feature is bent backward as depicted. The relative flexingof the fins in this fashion allows the fins without the locking feature(1108) to be inserted beneath the conical locking feature (1106) suchthat all are captured in the closed position as further depicted in FIG.13.

FIG. 13 depicts the additional elements of this embodiment as well asthe prepared cannula device. As shown, the embodiment includes a trocardevice having a handle (1302) with a shaft member (1306) extending fromthe proximal end to form a tapered distal end (1308). An anti-plungingdevice (1304) attaches to the shaft member (1306), and the tapereddistal end (1308) is inserted into the proximal end of the cannuladevice lumen. The anti-plunging device (1304) blocks the shaft memberdistal end (1308) from advancing past a first position as shown in thefigure by hidden lines in the body member (1102). This first positionprevents the shaft member distal end (1308) from contacting thecorrugated feature (1110) in the fins.

Once assembled, this embodiment may be utilized with a patient byinserting the distal end of the fin into an incision in the patient'sskin. Once the body member (1102) is fully inserted, the anti-plungingdevice (1304) is removed from the shaft (1306) and the trocar is furtherinserted past the first position to a second position. In the secondposition, the tapered distal end (1308) contacts the corrugated features(1110), applying force to the fins such that the captured fins aredislodged from beneath the locking feature (1106). The bias pressures ofthe fins then force the fins to return to the initial outward-biasposition, compressing the patient's tissue through which the cannuladevice was inserted (as in FIG. 14).

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive. Accordingly, the scope of theinvention is established by the appended claims rather than by theforegoing description. All changes that come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein. Further, the recitation of method steps does not denote aparticular sequence for execution of the steps. Such method steps maytherefore be performed in a sequence other than that recited unless theparticular claim expressly states otherwise.

We claim:
 1. A retractable cannula for surgical procedures, the cannulacomprising: a body member forming a lumen having a plurality ofoutwardly-biased fins extending therefrom, wherein each fin is inwardlyflexible and capable of being moved inward to a converged position byinsertion of a removable trocar into the lumen to allow insertion of thecannula into an incision in the body of a patient, and wherein each finof the inserted cannula is capable of being moved inward to theconverged position by insertion of a removable trocar into the lumen toallow subsequent removal of the cannula from the incision.
 2. Thecannula of claim 1, each fin further including a longitudinal slotformed along the lateral edges of the fin and extending along the lengthof the fin.
 3. The cannula of claim 1, each fin further including alongitudinal slot formed along the lateral edges of the fin andextending along the length of the fin, wherein the longitudinal slotsformed along the lateral edges of adjacent fins combine to engage acomplimentary feature on a trocar device to effect inward movement ofthe plurality of fins.
 4. The cannula of claim 1, each fin furtherincluding a longitudinal slot formed along the lateral edges of the finand extending along the length of the fin, the cannula furthercomprising: a trocar device including a handle and a shaft member,wherein the shaft member fits within the lumen and extends into thefins, the shaft member including at least one raised member per fin,wherein the raised member compliments the shape of the fin slot formedalong the edge of two adjacent fins, each raised member engaging thecomplimentary fin slot along the edge of the two adjacent fins to effectinward movement of the plurality of fins upon insertion of the trocardevice into the lumen.
 5. The cannula of claim 1, each fin furthercomprising an additional biasing device.
 6. The cannula of claim 1, eachfin further comprising an additional biasing device, wherein the biasingdevice is a shape memory alloy.
 7. The cannula of claim 1, each finfurther comprising an additional biasing device, wherein the biasingdevice is a shape memory alloy, and wherein the biasing device iscapable of reacting to the patient's body temperature such that thebiasing device outward biasing pressure increases with an increase inthe patient's temperature thereby increasing the compressive forces onthe patients surrounding body tissue.
 8. The cannula of claim 1, eachfin further including at least one longitudinal slot along the length ofthe fin inner surface.
 9. The cannula of claim 1, each fin furtherincluding at least one longitudinal slot along the length of the fininner surface, wherein the longitudinal slot engages a complimentaryfeature on a trocar device to effect inward movement of the plurality offins.
 10. The cannula of claim 1, each fin further including at leastone longitudinal slot along the length of the fin inner surface, thecannula further comprising: a trocar device including a handle and ashaft member, wherein the shaft member fits within the lumen and extendsinto the fins, the shaft member including at least one raised member perfin slot, each raised member engaging a complimentary fin slot to effectinward movement of the fins upon insertion of the trocar device.
 11. Thecannula of claim 1, at least one fin further comprising a lockingfeature for capturing the remaining fins thereby maintaining the fins ina converged position until unlocked manually by insertion of a trocardevice.
 12. A method for treatment of a patient utilizing a retractablecannula, the method steps comprising: providing a cannula having a lumenand a plurality of outwardly-biased inwardly flexible fins extendingtherefrom; inserting a trocar into the lumen to effect inwardconvergence of the outwardly-biased flexible fins; inserting theconverged fins of the cannula into an incision in the patient; andextracting the trocar from the lumen to allow the fins to return totheir outwardly-biased position within the patient, thereby compressingthe surrounding tissue and forming a port through which surgicalinstruments may pass.
 13. The method of claim 11, the method stepsfurther comprising: inserting the trocar into the lumen to effect inwardconvergence of the fins; and removing the cannula from the patient. 14.A method for treatment of a patient utilizing a retractable cannula, themethod steps comprising: providing a cannula having a lumen and aplurality of outwardly-biased inwardly flexible fins extendingtherefrom, the flexible fins having a locking feature that maintains thefins in a converged position; inserting a trocar into the lumen, thetrocar shaft having an anti-plunging device to limit its depth withinthe lumen; inserting the converged and locked fins of the cannula intoan incision in the patient; removing the anti-plunging device from thetrocar shaft and further inserting the trocar into the lumen to effectunlocking of the fins to allow the fins to return to theiroutwardly-biased position within the patient, thereby compressing thesurrounding tissue; and extracting the trocar from the lumen therebyforming a port through which surgical instruments may pass.